The present invention relates to a method and a device for preventing distribution of fire gases in a ventilating system that serves a number of fire compartments, the ventilating air, during normal operating conditions, having a certain predetermined direction of flow at the inlet side and the outlet side of said fire compartments.
From SE-B-442 338 a device adapted to prevent distribution of fire gases in a ventilating system is previously known. This device relies on the principle that self actuated non-return valves, arranged in the ducts of the ventilating system, are kept open by a pressure drop that is present over said valves, said pressure drop being generated by a fan device allotted to said ventilating system. Each of said valves are arranged to automatically close when the pressure drop ceases. If such a valve is arranged at the inlet side of a fire compartment and a pressure is developed in said fire compartment, e.g. in connection with a fire, said pressure may remove the pressure drop over the valve, said valve automatically closes and the supply of ventilating air to the fire compartment ceases. Air is sucked out through the valve at the outlet side as long as the fan device is operating. This sucked out air is not able to enter any other fire compartment due to the valve that is arranged at the outlet side of the other fire compartments.
The arrangement described above has the disadvantage that an accurate mounting of the valves is necessary since their function relies on the attraction of gravity. Further, energy losses are present if the valves are to open at air flows of low velocity.
Ventilating systems with non-return valves are previously known from SE-B-459 522 and SE-B-460 434, said non-return valves being developed from the device according to SE-B-442 338, said device thus aiming at the prevention of distributing fire gases. The further developed ventilating systems are also aiming at the prevention of fire distribution. In order to realize this the non-return valves are equipped with a heat sensitive means, e.g. a fuse, that releases a closing of the non-return valves when the temperature adjacent the valves exceeds a certain value.
It is also previously known to register the presence of fire gases in a ventilating system by providing smoke detectors in the ducts of the ventilating system. However, a number of disadvantages are connected with said smoke detectors. Firstly, it should be mentioned that it is difficult to position the smoke detectors, especially if they are to detect smoke from several fire compartments. A further disadvantage is that the function of the smoke detector depends on the type of smoke that is generated, i.e. the smoke detector indicates only for certain type/types of smoke. This means that it is extremely complicated to check whether a smoke detector functions. Further, the smoke detector normally does not indicate until the duct is filled with smoke. Unsuccessful positioning or a quick fire progress may cause extensive fire damages in other fire compartments. In this connection it should also be considered that the smoke detector is comparatively expensive.
A primary object of the present invention is to define a method and a device that in an effective way prevent distribution of fire gases in a ventilating system.
According to a preferred embodiment the principle of the present invention may also be used in connection with varying air velocities in the ventilating system.
A further object of the present invention is that indication in order to prevent fire distribution should also be effected.
At least the primary object of the present invention is realized by means of a method and a device that have been given the features of the appending independent claims. Preferred embodiments of the invention are defined in the dependent claims.